This invention relates to a process for removing chloride impurities from TiO.sub.2. A pigmentary TiO.sub.2 can be produced by oxidizing TiCl.sub.4 at elevated temperatures such as that disclosed in U.S. Pat. No. 2,488,439. The TiO.sub.2 product which is entrained in gaseous reaction products emerges from the oxidation reactor at 700.degree.-1600.degree. C. and it can be cooled to a temperature ranging from 300.degree.-800.degree. C. by the procedures disclosed in U.S. Pat. Nos. 2,833,637 and 2,721,626. The cooled TiO.sub.2 can be separated from the gaseous products by any suitable separation device such as a centrifuge or a cyclone. The TiO.sub.2 product recovered from the separation contains a low concentration of untreated chloride impurities such as TiCl.sub.4, TiOCl.sub.2, HCl, and Cl.sub.2 adsorbed on the surface of the TiO.sub.2. Usually, about 0.1-0.4 weight percent total chlorides, expressed as HCl, is present in the product. These chloride impurities must be removed from the TiO.sub.2 product because the TiO.sub.2 product containing the chloride impurities cannot be used in many pigmenting applications such as paints, enamels, and finishes since the chloride impurities are incompatible with and usually react with vehicles in which the TiO.sub.2 is dispersed.
In the past, calcination at 600.degree. C. for about 2 hours has been used to remove chloride impurities from TiO.sub.2. Even though this process is effective in removing impurities, it requires much time and expense.
Two other methods for the removal of chlorides from TiO.sub.2 are described in U.S. Pat. No. 3,253,889 to Wildt et al., and British Pat. No. 1,003,957. The process in U.S. Pat. No. 3,253,889 relates to subjecting the TiO.sub.2 while in aerosuspension at a concentration of 0.1-20 pounds of TiO.sub.2 per cubic foot of aerosuspension to direct contact for a period of less than 5 minutes in a treating zone maintained at a temperature of 400.degree.-1000.degree. C. with a gaseous treating agent selected from water vapor, air, oxygen, and mixtures thereof. The process in British Pat. No. 1,003,957 relates to introducing highly dispersed oxides of silicon, aluminum, titanium, and/or zirconium into a treatment chamber in parallel relationship with a stream of steam which may be diluted with an inert gas so as to form a turbulent suspension of oxides in the steam, which suspension is heated at a temperature from 450.degree.-1000.degree. C. and removing the treated oxides and the resultant gases containing impurities from the end of the treatment chamber opposite to the end at which they were introduced. However, in both of these processes the time required to remove impurities from the prducts is relatively long. Thus, there is a need for a process which will remove chloride impurities from TiO.sub.2 more rapidly than any of the above-described processes.